Metal stretching press



Sept. 1,1942. 11. F; MaCMILLiN ETAL; 2,294,676

METAL STRETCHING PRES S Original Filed March 25, 1940 Arron/5v:

Patented Sept. 1, 1942 METAL STRETCHING PRESS Howard F. MacMillin, Mount Gilead, and Warren R. Tucker, Dayton, Ohio, and Reider Thoreson, Birmingham, Mich., assignors to The Hydraulic Development Corp., Inc., Wilmington, Del., a

corporation of Delaware Original application March 25, 1940, Serial No. v

325,780. 'Divided and this application November 28, 1940, Serial No. 367,615

6 Claims. .(Cl. 113-45) The present invention relates to hydraulic presses, and particularly to presses of the type that employ mechanism for clamping the workpiece to the press.

This application is a division of our application SerialNu-mber 325,780 filed March 25, 1940 and entitled "Metal stretching press."

In certain forms of hydraulic drawing presses it is sometimes necessary to clamp the sheet of metal to the bed or top plate of the press. Various methods for doing this have been proposed, and practically all of .these methods depend on the use of clamping or gripping forces derived from pneumatic cylinders, electric motors or hand-power-operated through levers. The use of these forces obviously requires a source of energy different from that employed in the press, which adds to the expense of the press as a whole, also to the installation and to the complexity of operation. Furthermore, the powermultiplying levers are often of a complicated mechanical character due to the manner and direction in which the force is applied.

Presses of this general type quite frequently require precise timing between the clampingand pressing forces, particularly to insure that the gripping effect is provided before the metal is worked. Obviously, this timing requirement is difficult to achieve and maintain, where separate sources of energy are employed for the gripping modate the drawing or forming operation, it is often difficult to make the necessary adjustments of the prior-art clamps to not only insure proper timing but also the proper amount of slippage, Y

and it is harder yet to change the adjustments of the lamps individually to produce local pressing The primary object of the present invention is t0. provide a hydraulic press which is adapted to grip the work with or without slippage, and to eliminate all of the disadvantages in connection with prior-art presses of this general character.

Another object is to provide a press in which the ippin or blank holder jaws are acted upon by the same source of power which is employed for'operating the press. W

A further object is to provide a hydraulic press direct hydraulic pressure, thus insuring perfect coordination between the press and the workclamping mechanism. Only a single source of hydraulic power is required for these two purposes, so that when pressure is applied to the fluid of the press and the clamping mechanism is simultaneously subjected to the pressure of the same-fluid.

A still further object is to providea hydraulic 4 press in which the workpiece is gripped at a number of difierent areas throughout the surface of the workpiece, and ready adjustment may be the various workpiece and receiving their power from the same source of pressure flui operates the press. Each of these pistons reciprocates incylinders, the pressure of which may be adjusted, as a whole or individually in orderto provide the necessary general or specialclamping effects.

Qther objects and features will be apparent as the specification is perused in connection with the accompanying drawing.

In the drawing:

Figure 1 is a perspective viewwith a part broken away and in section, of a hydraulic press improved in accordance with the present invention.

Figure 2 is a sectional view of the press shown in Figure 1 except that the platen, the plunger and some of the immediately associated parts are shown in elevation.

The press is supported on a fiat base member I of rectangular configuration having countersunk holes 2 at the corners thereof, for receiving a number of strain rods 3 threaded at each adapted to receive die strips 1 bolted or other-.

wise secured thereto. The base member I is provided with an upstanding cylinder 8 at'the center,

in which the clamping efiects are obtained by 55 in which a piston 9 and plunger l0 are adapted to reciprocate. The plunger ID has a turned-down shoulder II at the top, and this shoulder portion carries the usual platen l2 and the punch l3.

Surrounding the shouldered portion and rigidly secured thereto there is a hub Hi, from which radiate, at equi-distant positions, four wing-shaped members I5 which take the general form of an tional lip 28.

a=configuration, and are constituted of fiat pieces of? metal terminating in a. number of cylinders it. These cylinders are bored, as indicated at it, from the'top and closed at the bottom. The

bores ll slidably receive pistons i8, which are threaded at the top into'a rectangular gripping plate l9. Nuts 23 may be employed to assure which receive guide rods 22 which are firmly secured to the lips by nuts23.- Th lower ends of the rods 22 move through openings which are provided in extensions 3 formed on the wing members it. The rods at the bottom may carry nuts 25. Thearrangement is such that the wi members It are adapted to slide upwardly over the'rods 22, the nuts 25 assisting in determining the lower limit of travel ofthe wing elements.

The hydraulic system includes the pump 2t,

the oil tank 2'3, the four-way valve 28 and the high pressure line 29 and the low pressure line 3d. There is a pipe 33 extending from the upper surface of the valve 28 to the lower endof the These lips 2i contain openings upwardly with greater force, thereby increasing the clamping effect at the metal sheet.

In the event that this pressure becomes excessive, surplus fluid in the bores i1 is permitted to pass from the inlets 33 into the vertical pipes 38 where they operate the relief valves 31, and this fluid is then permitted to return to the tank through the conduits 36. The clamping effect at the plates 5 and I9 is entirely completed at the time the plunger i6 is moved to such a height as to cause the punch 3 to contact with the metal sheet. Continued movement of the punch will cause the requited deformation of the metal sheet, in accordance with the shape and size of the opening between the upper die strips 7 and as also determined by the shape of the punch. It is apparent that during the upward movement of the plunger ill the wings l5 slide upwardly over the guide rods 22. The fluid which is entrapped at the rear side of the piston 3 finds ready access to the low pressure side ofthe pump or atanl:

through the pipes 32 and 30. When the punch has reached its upper-limit of travel, as determined by the operatorbr in any other suitable manner, the rod 42 is moved to the right, which is the position shown in Figure 2. Under these conditions high pressure fluid passes from the pipe-.29 to the pipe 32 which leads to the rear cylinder 8. A length of pipe 32 connects the v space to the rear of the piston 9 with the upper surface of the valve 28. There is a fluid inlet opening 33 at the lowermost portion of each clamping cylinder IG, and this opening is connected to the'high pressure side of the pump through a flexible pipe 34 and a check valve 35. It will be noted that this valve is so arranged 'as to permit fluid to pass inwardly toward the bore I! of the olampingcylinders. It will be understood that communication is made between the high pressure side of the pump and the lower portions of all of the clamping cylinders through their respective check valves 35. A flexible pipe 36 is taken from the low pressure side of the pump or the oil tank 21, through an adjustable pressure relief. valve 31. and a short length of pipe 38, to the opening 33. This valve may be conveniently secured to the upper portion of the I ,cyl'inder in order lac-facilitate adjustment. There is a choke valve39 positioned in the low pressure line 40 leading from the valve 28.

The parts are shown at the instant that the main piston 3 has reached its lower limit of travel, and it is assumed that the finished article formed by the previous pressing operation has been removed from the machine. A fresh metal sheet l l is placed in position within the space between the die strips 1. The operator then causes the rod 42 of the four-way valve tobe moved to the left, causinghigh pressure fluid to be introduced into the pipe 3|. As the pressure below the main piston increases, the plunger l-B will rise and will carry the wing members l5 upwardly together with the clamping cylinders l6. These cylinders have been previously filled with fluid through the conduit 43 and the check valves 44. Consequently, as the cylinders move side of the piston 9. At the same time the space in front of the piston is in communication with the tank through the pipes 3-l 29, the choke valve 39 and the pipe 30. The choke valve 39 is for the purpose of limiting the rate at which the fluid is exhausted from the front side of the main piston during thed-ownward movement of that piston.

As the plunger 10 moves downwardly, due to the pressure fluid passing through the pipe 32, it carries with it the punch l3 and the wings IS. The cylinders l6 carried by the wings also move downwardly, which tends to reduce the pressure tion with the high pressure side of the pump tireless there is suflicient pressurestill exercised through the flexible pipes 34, and further that the only way the fluid can escape is through the relief valves 31 which are set to operate onlyabove a predetermined pressure. Consequently, while the pressure is reduced to some extent by the.

movement downwardly of the cylinders l6, neveron the plungers l8 tomaintain sumcient clamping effect between the plates 5 and 19 when the punch 13 breaks contact with the formed metal article. As the plunger l0 continues its downward. movement the cylinders l6 travel downwardly a corresponding distance, which eventual ly will reduce the pressure of the contained fluid j to such a value as to permit the plate l9 to descend of its own weight. Such a condition is under the direct control of the adjustments accorded-the relief valves 31, and preferably takes place only after the punch 13 has moved an appreciable distance away from the work.

' Thus it is evident that clamping pressure is assured at atime prior to when the punch l3 contacts the metal sheet during the working stroke and is also maintained for a suflicient length of with respect to the plungers 18 the fluid within time after the punch starts to descend. It is further apparent that the time relation between these clamping. effects and the movement of the punch can be accurately correlated and adjusted by proper control of the pressure relief valves 31.; The adjustment of'these valves also I affects the intensity'oi the clamping force so that special and local clamping effect can be obtained,

plunger in each of said cylinders, a punch carried by the plunger in the pressing cylinder and adapted to move upwardly against the metal sheet which is to be formed into the article, the clamping cylinder being secured to the plunger of the pressing cylinder, a clamping plate secured to the metal sheet in position during the pressing operation, and means for applying pressure fluid separately to the lifting side of the plungers in the main and clamping cylinders respectively whereby the punch is caused to contact with the metal sheet and the plunger in the clamping cylinder moves upwardly to move the clamping plate into clamping position.

2. Ahydraulic press for fabricating articles out of sheet metal, said press comprising a main pressing cylinder and a plurality of clamping cylinders symmetrically arranged about the pressing plunger of the clamping cylinder for holding the cylinder, a plunger in each of said cylinders, a

punch carried by the plunger of the pressing cylinder and adapted to move upwardly against the metal sheet which is to be formed into an article, wing members extending outwardly from the plunger in the pressing cylinder and secured to the clamping cylinders whereby the clamping,

cylinders are caused to move upwardly when the plunger of the main cylinder rises, a clamping plate secured to the plungers of the clamping cylinders for holding the metal sheet in position duringthe pressing operation, a source of pressure fluid, a conduit extending directly from the high pressure side of said source to the working side of the'plungers in the clamping cylinders whereby the pressures maintained in said'clamping' cylinders are'equal, and means for applying fluid pressure from said source to the lifting side of the plunger in the main cylinder whereby the main plunger and the clamping cylinders are caused to be elevated and the pressure of the fluid in the clamping cylinders rises to such value as to cause the clamping plungers to be moved upwardly and to force the clamping plate againstsaid sheet of metal so that the metal sheet is clamped in position before the punch carried by the main plunger contacts with said sheet. I

3. A hydraulic press for fabricating articles out of sheet metal, said press comprising a main pressing cylinder and'a-plurality of clamping cylinders symmetrically arranged about the pressing cylinder, a plunger in each of said cylinders, a punch carried by the plunger of the pressing cylinder and adapted to move upwardly againstthe metal sheet which is to be formed into an article, wing members extending outof the clamping cylinders for holding the metal sheet in position during the pressing operation, a source of pressure fluid, conduits extending directly from the high pressure side of said source to the working side of the plungers in the clamping cylinders, pressure relief valves connected respectively between said conduits and the low pressure side of said source whereby the pressures maintained in said clamping cylinders are equal, and means for applying pressure fluid from said source to-the lifting side of the plunger in the main cylinder whereby the main plunger and the clamping cylinders are caused to be elevated and the pressure of the fluid in the clamping cylinders rises to such value as to cause the clamping plungers to be moved upwardly and to force the clamping plate against said sheet of metal so that the metal sheet is clamped in position before the punch carried by the main plunger contacts with said sheet, said pressure relief valves being of adjustable character so that the pressure within the clamping cylinders will not exceed a predetermined work-slipping value whereby slippage is permitted between the metal sheet and the clamping plate in order to accommodate the stretch of the metal during the forming operation.

4. A hydraulic press comprising a main pressing cylinder and an auxiliary clamping cylinder, a plunger in each of said cylinders, a punch carried by the main plunger for forming a metal sheet into a desired shape, a clamping plate carried by the clamping plunger for holding the sheet in position during the forming operation, a mechanical connecton between the main plunger and the clamping cylinder, a source of pressure fluid and a control valve therefor, said valve being provided with high pressure and low pressure openings which communicate with saidtively for the fluid in an alternate manner depending on the position of the piston within said valve, a conduit extending from the ingress opening to the working side of the main plunger, a second conduit extending from the egress opening to the rear side of the main plunger, a third conduit extending directly from the high pressure side of said source to the working side of the clamping plunger, and means including a relief .valve connected to said third conduit for limiting the fluid pressure in the clamping cylinder to a work-slipping value as the main plunger is lifted by the fluid passing through the conduit which extends from said ingress opening and carrying with said plunger the clamping cylinder. 7

5. A hydraulic press comprising a main pressing cylinder and an auxiliary clamping cylinder, a plunger in each of said cylinders, a punch carried by the main plunger for forming a metal sheet into a desired shape, a clamping plate carried by the clamping plunger for holding the sheet in position during the forming operation, a mechanical connection between the main plunger and the clamping cylinder, a source of pressure source, a piston in said valve, said valve also being provided with a pair of openings which are adapted to be an ingress and an egress respectively for the fluid in an alternate manner depending on the position of the piston within said valve, a conduit extending from the ingress opening to the working side of the main plunger, a second conduit extending from the egress opening to the rear side of the main plunger, a third conduit extending directly from the-high pressure side of said source to the working side of the clamping plunger, and means including a relief valve connected to said third conduit for limiting the fluid pressure in the clamping cylinder to a work-slipping value as the main plunger is lifted the punch contacts said sheet as the main plunger is being lifted. I

' 6. A metal stretching press for stretching articles of complicated shape from sheet metal, said press comprising a main pressing cylinder and a clamping cylinder, a plunger in each or said 0311- inders, a punch carried by the plunger in the pressing cylinder and adapted to move upwardly against the metal sheet which is to bel'forrned into the article, the clamping cylinder being secured to the plunger of the pressing cylinder, a clamping plate secured to the plunger of the clamping cylinder for holding the metal sheet in position during the pressing operation, a source 01 pressure fluid, a conduit extending directly from the high pressure side of said source tothe working side of the plunger in the clamping cylinder, and means for applying fluid pressure from said source to the lifting side of the plunger I in the main cylinder whereby the main plunger and the clamping cylinder are caused to be ele vated and the pressure of the fiuid in the clamr 'ing cylinder rises to such a value as to cause the clamping plunger to he moved upwardly and to force the clamping plate against said sheet cf metal.

HQWARD F. MACMILLIN. WARREN R. TUCKER. REEDER THORESON. 

